Influence of asymmetric well/barrier layers on the performance of InGaN quantum well lasers

The structural parameters of the quantum well have a very important influence on the performance of InGaN laser, including output power, optical field distribution, electron leakage, etc., so it needs to be considered in the design. The photoelectric performance of InGaN/(In)GaN quantum well lasers with varying thickness of quantum well/barrier layers are theoretically investigated with the simulation program Crosslight. For three In0.15Ga0.85N/GaN quantum wells violet laser diode (LD) with lasing wavelength around 410 nm, the performance of threshold current and optical output power of the laser degenerates with the uneven well thickness. This is attributed to the deterioration of the carrier distribution and the mode gain in quantum wells. When the quantum well structure adopts barrier layers with non-uniform thickness, the threshold current of InGaN quantum well laser degenerates a little while the lasers' optical output power increase slightly. Based on the In0.15Ga0.85N/In0.02Ga0.98N quantum well, the larger refractive index difference between the barrier layer and the well layer significantly improves the distribution and concentrates of the optical field near the active region. Meanwhile, compared with In0.15Ga0.85N/GaN structure, In0.15Ga0.85N/In0.02Ga0.98N quantum well laser is more effective in reducing the electron leakage. Moreover, the output power of gradually thickening barrier laser achieves 2.6 times that of the In0.15Ga0.85N/GaN symmetric quantum well structure. Our results prove that the asymmetric quantum wells with higher refractive index and gradually thickening barrier layer are beneficial to realize low threshold current and high output power laser.